Integrated electrical circuits are typically tested prior to final dicing and packaging. Such testing usually entails making temporary electrical contact to contact pads on the circuit or chip being tested. Probes or probe arrays are commonly employed to make such temporary electrical contact. Probes or probe arrays for this application have been under development for many years, since the ongoing technological evolution of chips and integrated circuitry to ever-smaller dimensions tends to raise problems which require new probing solutions.
For example, vertical probes have evolved significantly over time. In a vertical probe, at least a substantial portion of the probe is aligned along the vertical direction, where “vertical” is conventionally taken to the direction of probe travel when making contact. Vertical probes can provide improved control of scrub motion of the probe tip relative to the contact pad as contact is made, e.g., as described in U.S. Pat. No. 7,148,709 by the present inventor. Such improved control of scrub motion is increasingly important as contact pad dimensions decrease. Various aspects of arrays of vertical probes are also considered in U.S. Pat. No. 7,148,709, as well as in U.S. Pat. Nos. 6,443,784, 6,731,123, and 6,847,221.
Vertical probes often have a well-defined probe plane, such that deformation of the probe during contact occurs primarily in the probe plane without significant lateral (i.e. out of plane) motion. This situation is preferred in practice, because it allows an array of vertical probes to be closely spaced in a direction perpendicular to the probe plane, thereby facilitating making contact to a corresponding array of closely spaced contact pads. As long as the probe deformation is in-plane, undesirable contact between adjacent probes as a result of probe deformation during contact will not occur.
However, this approach can encounter difficulty as the contact pad spacing decreases, since decreased probe width (to accommodate the reduced contact pad spacing) can lead to an undesirable tendency of the probes to laterally deform. Such lateral probe deformation is highly undesirable, since it can lead to electrical contact between different probes of the same probe array.
Accordingly, it would be an advance in the art to provide probing of closely spaced contact pads with a vertical probe array having a reduced tendency for probes to laterally deform.